Purification of fluids and control of solute concentrations through selective degasification

Abstract

Degassing is accomplished by driving a gas-containing solution to a subatmospheric pressure approximately equal to the solution vapor pressure, and maintaining the subatmospheric pressure notwithstanding evolution of gas from the solution. This may be accomplished using a vacuum tower arrangment whereby a column of the gas-containing liquid is drawn to the maximum physically attainable height. So long as the vacuum is coupled to the liquid column above this height (generally on the order of 34 feet, depending on the ambient temperature and the composition of the liquid), the liquid will not be drawn into the vacuum, which creates a non-equilibrium region of extremely low pressure above the liquid that liberates dissolved gases. Moreover, liquid introduced into the low-pressure region above the column will fall onto the column without entering the vacuum system. As a result, the region above the column represents an interaction region within which gas will be stripped from an incoming liquid as it falls toward the column.

What is claimed is:  
     
       1. A method of degassing a solution having a vapor pressure, the method comprising the steps of: 
       a. driving the solution to a subatmospheric pressure;  
       b. maintaining the subatmospheric pressure notwithstanding evolution of gas from the solution by applying, without contact, a continuous vacuum to the solution, the continuous vacuum drawing the solution into a column to a maximum physically attainable height; and  
       c. degassing by feeding the solution into the vacuum above the column.  
     
     
       2. The method of claim  1  wherein the solution comprises at least one ionic species in equilibrium with a dissolved gas, degassing precipitating an ionic species by preventing chelation. 
     
     
       3. The method of claim  1  wherein the solution comprises a substance present as a dissolved gas in equilibrium with at least one non-gas dissolved species, maintenance of the subatmospheric pressure driving the equilibrium toward the dissolved gas, removal of which depletes the solution of the substance without addition of solids. 
     
     
       4. The method of claim  3  wherein the substance is a halogen. 
     
     
       5. The method of claim  1  wherein the solution comprises a dissolved reactive gas in equilibrium with a non-volatile soluble species formed therefrom, degassing decreasing the concentration of the non-volatile soluble species. 
     
     
       6. The method of claim  5  wherein the dissolved reactive gas and the non-volatile soluble species are selected from the group consisting, respectively, of (a) gases that are dibasic or reversibly react with water to form dibasic acids, and (b) a corresponding dibasic acid salt. 
     
     
       7. The method of claim  6  wherein: 
       a. the gases that are dibasic or reversibly react with water to form dibasic acids are themselves selected from the group consisting of carbon dioxide, hydrogen sulfide, hydrogen selenide, carbon oxysulfide, carbon disulfide, and sulfur dioxide; and  
       b. the corresponding dibasic acid salt is selected from the group consisting of (i) a carbonate salt of at least one of ammonia, barium, calcium, chromium, iron, lithium, magnesium, manganese, nickel, potassium, sodium, strontium, and zinc; (ii) a divalent salt of hydrogen sulfide and ammonia, calcium, lithium, potassium, sodium, or strontium; (iii) a divalent salt of hydrogen selenide and ammonia, lithium, potassium, and sodium; (iv) a thiocarbonate alkaline earth metal or alkali metal salt of carbon oxysulfide; (v) a dithiocarbonate alkaline earth metal or alkali metal salt of carbon disulfide; and (vi) a sulfite salt of ammonia, calcium, lithium, magnesium, potassium, sodium, or strontium and sulfur dioxide.  
     
     
       8. The method of claim  5  further comprising the steps of: 
       a. prior to degassing, drawing a gas mixture into the solution, the gas mixture containing the reactive gas which reacts to form the non-volatile soluble species, the reactive gas substantially fully entering solution;  
       b. venting components of the gas mixture that have not entered solution;  
       wherein 
       c. degassing reduces the concentration of the non-volatile soluble species, thereby increasing the capacity of the solution for uptake of the reactive gas.  
     
     
       9. The method of claim  8  wherein: 
       a. the reactive gas is drawn into the solution and the other gas components are vented in a first recirculating subsystem;  
       b. the solution is degassed in a second recirculating subsystem; and  
       c. a portion of the solution from the first subsystem is continually conveyed to the second subsystem, and a balancing portion of the degassed solution from the second subsystem is returned to the first subsystem.  
     
     
       10. The method of claim  9  wherein the first subsystem comprises a venturi for drawing the gas mixture into the solution, and the second subsystem comprises a vacuum system for applying, without contact, a continuous vacuum to the solution. 
     
     
       11. The method of claim  1  further comprising the steps of: 
       a. creating the vacuum by recirculating liquid through a venturi, the venturi being fluidly coupled to the solution above a surface of the column at the maximum physically attainable height; and  
       b. degassing by feeding the solution into the vacuum above the surface of the column.  
     
     
       12. The method of claim  11  wherein the venturi is powered by a recirculating stream of liquid, the recirculating liquid comprising a material for reacting with gas drawn from the solution. 
     
     
       13. The method of claim  12  wherein the material comprises microorganisms. 
     
     
       14. The method of claim  11  wherein the solution to be degassed is fed through a set of spiral vanes that cause the solution to spin at high velocity. 
     
     
       15. The method of claim  1  further comprising the steps of: 
       a. in a first subsystem,  
       i. providing an aqueous mixture comprising a solids fraction and an unwanted, partially dissolved component;  
       ii. introducing a solubilizing gas into the mixture to further solubilize the unwanted component;  
       iii. removing the solids fraction substantially free of the unwanted component to yield the solution to be degassed;  
       b. performing the degassing steps in a second subsystem, the degassing step producing the solubilizing gas and precipitating the unwanted component;  
       c. separating the unwanted component; and  
       d. feeding the solubilizing gas obtained by degassing into the first subsystem.  
     
     
       16. The method of claim  15  wherein the first subsystem comprises: 
       a. a first venturi for drawing the aqueous mixture into the first subsystem;  
       b. means for recirculating the mixture through the first subsystem; and  
       c. a second venturi fluidly coupled to the second subsystem for creating therein a continuous vacuum, the continuous vacuum drawing the solution in a column to a maximum physically attainable height, the degassing being accomplished by feeding the solution into the vacuum above the surface of the column.  
     
     
       17. The method of claim  16  wherein the solution to be degassed is fed through a set of spiral vanes that cause the solution to spin at high velocity. 
     
     
       18. The method of claim  15  wherein the unwanted, partially dissolved component of the aqueous mixture is: 
       a. (i) selected from the group consisting of phosphates, sulfates, arsenates, arsenites, and carbonates of a divalent, trivalent, or tetravalent metal and (ii) rendered soluble by addition of carbon dioxide or sulfur dioxide; or  
       b. at least one divalent or polyvalent metal salt rendered soluble by addition of ammonia to form chelation complexes.  
     
     
       19. Apparatus for degassing a solution having a vapor pressure, the apparatus comprising: 
       a. means for driving the solution to a subatmospheric pressure;  
       b. means for maintaining the subatmospheric pressure notwithstanding evolution of gas from the solution, said means comprising a vacuum apparatus configured to apply, without contact, a continuous vacuum to the solution, the continuous vacuum drawing the liquid to a maximum physically attainable height and  
       c. a feeder for introducing the solution into the vacuum above said height to effect degassing of the solution.  
     
     
       20. The apparatus of claim  19  wherein the solution comprises a substance present as a dissolved gas in equilibrium with at least one non-gas dissolved species, maintenance of the subatmospheric pressure driving the equilibrium toward the dissolved gas, removal of which depletes the solution of the substance without addition of solids, the apparatus further comprising: 
       a. means for drawing a gas mixture into the solution prior to degassing, the gas mixture containing a reactive gas which reacts to form a non-volatile soluble species, the reactive gas substantially fully entering solution; and  
       b. means for venting components of the gas mixture that have not entered solution;  
       wherein 
       c. degassing reduces the concentration of the non-volatile soluble species, thereby increasing the capacity of the solution for uptake of the reactive gas.  
     
     
       21. The apparatus of claim  20  further comprising: 
       a. a first recirculating subsystem in which the reactive gas is drawn into the solution and the other gas components are vented in; and  
       b. a second recirculating subsystem in which the solution is degassed, a portion of the solution from the first subsystem being continually conveyed to the second subsystem, and a balancing portion of the degassed solution from the second subsystem being returned to the first subsystem.  
     
     
       22. The apparatus of claim  21  wherein the first subsystem comprises a venturi for drawing the gas mixture into the solution, and the second subsystem comprises a vacuum system for applying, without contact, a continuous vacuum to the solution. 
     
     
       23. The apparatus of claim  19  wherein: 
       a. the vacuum apparatus comprises a venturi through which liquid is recirculated to create the vacuum, the venturi being fluidly coupled to the solution above a surface thereof at the maximum physically attainable height; and  
       b. degassing is accomplished by feeding the solution into the vacuum above the surface of the column.  
     
     
       24. The apparatus of claim  23  further comprising a recirculating stream of liquid powering the venturi, the recirculating liquid comprising a material for reacting with gas drawn from the solution. 
     
     
       25. The apparatus of claim  23  further comprising a set of spiral vanes, the solution to be degassed being fed through the vanes to thereby cause the solution to spin at high velocity. 
     
     
       26. The apparatus of claim  19  further comprising: 
       a. a first subsystem configured to:  
       i. provide an aqueous mixture comprising a solids fraction and an unwanted, partially dissolved component;  
       ii. introduce a solubilizing gas into the mixture to further solubilize the unwanted component; and  
       iii. remove the solids fraction substantially free of the unwanted component to yield the solution to be degassed;  
       b. a second subsystem for performing the degassing, the degassing producing the solubilizing gas and precipitating the unwanted component;  
       c. means for separating the unwanted component; and  
       d. means for feeding the solubilizing gas obtained by degassing into the first subsystem.  
     
     
       27. The apparatus of claim  26  wherein the first subsystem comprises: 
       a. a first venturi for drawing the aqueous mixture into the first subsystem;  
       b. means for recirculating the mixture through the first subsystem; and  
       c. a second venturi fluidly coupled to the second subsystem for creating therein a continuous vacuum, the continuous vacuum drawing the solution in a column to a maximum physically attainable height, the degassing being accomplished by feeding the solution into the vacuum above the surface of the column.  
     
     
       28. The apparatus of claim  27  further comprising a set of spiral vanes, the solution to be degassed being fed through the vanes to thereby cause the solution to spin at high velocity.